Duplex radio communication



, Jime5,192s. 13572355 ,P. WARE DUPLEX RAI DIO COMMUNICATION Fil ed' July 5. 1922 s Sheets-Sheet 1 INVENTO z 75 2 f ZATTORNEY June 5, 1928. 1,672,855

P. WARE DUPLEX RADIO coummxcnron Filed July 5. 1922 a Sheets-Sheet 2 IN VEN TOR 0 "J ATTORNEY June 5, 1928. 1,672,855

P. WARE DUPLEX RADIO GOI IMUNICATION Filed July 3; 1922 5 Sheets-Sheet a K/lacyc/ea per sec. 6I/AV5- 0 Kilo eye/u p 0- no.

OI/Al/E v4 INVENTOR A TTORNE Y v Patented June 5, 1928.

UNITED STATES PAUL WARE, on NEW PATENT OFFICE.

YORK, N. Y., ASSIGNOR TO WARE RADIO, INC., 01 NEW YORK, N. Y., A CORPORATION OF DELAWARE.

DUPLEX RADIO oommunioarron.

Application filed July 3, 1922. Serial No. 572,405.-

This invention relates to duplex radio communication and has for its object to enable two stations each having separate receiving and transmitting elements at the same location to simultaneously communicate,'-without having the receiver paralyzed by the relatively powerful transmitter cent thereto. It is the practice in many of the systems in use at present to either widely separate the receiver and transmitter of a station of more than'nominal power for simultaneous communicatioiucr else to 'cut out one while the other is operating, which does not permit simultaneous communication.

Bythis invention only such separation of a few feet between transmitter and receiver as may be had in the same building is necessary in order to provide sinmltaneous communication over distances up to severe hundred or more miles.

Other important objects of this invention are to improve upon the customary transmitting and receiving efliciencies, to eliminate the radiation of harmonicsand to so increase the selectivity of the receiving apparatus that 'otlice to office radio communication between wi'dely situated large cities, heretofore considered impracticable for many reasons, is now a practicable achieve- ,ment.

It is found that the customary interfer ence from other radio stations, and interferences and racket from induction customarily encountered in-attempting. to operate receiving stations in factory buildings,'etc., in the centers of large cities is greatly min imized or removed altogether by the receiving arrangement hereinafter described. It is also found by this invention that in-- terference from atmospheric electricity or static. is considerably minimized.

This invention consists essentially in trans-- mitting continuous Waves of one frequency from an elevated radiating system, While simultaneously receiving another frequency by means of a specially designed and con structed coil receiving set situated nearby.

I have found that the ordinary coil re ceiving set is inoperable in the proximity of a powerful transmitter, onanywhere near the same operating frequency, on account of paralysis of the receiving circuit by the adjacent transmitter, I have found. however, that a timed coil receiving element customarily found in radio receiving systoms. An electrostatic shield surrounding the small coil element will permit of still closer physical and frequency operation. Positioning of the coil element with respect to the transmitting system, that is, With a flat side towards the transmitter, also tends to permit of closer operation, but the selectivity of this receiving system is such that when operated in connection with a transmitting equipment having the characteristics described herein, no critical positioning is found to be necessary. In fact under quite usual operating conditions it is found that the receiving coil may be pointed directly at the transmitter antenna lead-in, but there is obviously advantage in not doing this The coil should, of course, point approximately towards the distant communicating station for best reception.-

Almost any type of transmitter may be used, but a preferred form of highly efiicient master oscillator circuit employing vacuum tubes is shown herein.

The invention will be morefully understood in connection with the description of the accompanying drawings wherein:

Fig. 1 is a general diagram,

Fig. 2 is a diagram of the transmitting circuit,

Fig. 3 is a diagram of a receiving circult.

Fig. 4 is a partial resonance curve of an ordinary type of receiver,

Fig. 5 is another portion of the curve of Fig. 4, and

Fig. 6 is a resonance curve of a receiver according to this invention.

Referring to Fig. l, 1 represents the elevated transmitting antenna supported by masts 2, the lead-in 13 passing through insulator in the roof 15 of the building 14, to

transmitting unit 4. Transmitting ground connection is made at 5. 6 represents the' coil receiving set, complete.

specifically indicates a switch for turning oflf and on the transmitter and 10 indicates a common wire telegraph key with side lever. 4

Most any type of transmitting circuit may give'satisfactory results, but the employment of powerful vacuum tubes is preferred 'inasmuch as they are the most readily obtainable means for securing pure waves. Fig. 2 is a diagram of a transmitting circuit which gives excellent results in this system. Referrin to the figure, theleft hand tube MO and its accompanying circuit represents a master oscillator used to drive the two right hand power amplifier tubes PA, and

to set the frequency of the transmitted waves and maintain their frequency constant independently of changes in the antenna circuit constants. 7 represents five diiferout high fr uency choke coils, 8 are three blocking cori d ensers while 18 are grid-leak resistances. 16 are gridplate oscillation condensers in the master oscillator circuit, and 17 is a variable inductance. 19 is a condenser the size of which varies the amount of excitation which the master oscillator imparts to the power amplifiers. 20 are ammeters for indicating the plate current to the power amplifier tubes and 21 is a variable choking unit for the purpose of suppressing undesirable oscillations at this point, and which greatly increases the customary efficiency of such a circuit. 22 is an A. C. generator for furnishing filament heating current. 28 is a potentiometer across the generator having a central or neutral point, which constitutes the ground of the circuit. From this neutral point to both sides of the filaments. are condensers of equal size for passing high frequency by potentiometer 23 to each side of the filaments equally. This method not only effectively removes the A. C. hum from the emitted waves but also lengthens filament life by equalizing the current to each side of the filament. 24 is an A. C. voltmeter across the filaments which is a better'filament indicator for this circuit than a series ammeter. 25 is a high voltag D. C. generator having its armature skew slotted about three-quarters of its slot pitch. This skew slotting in connection with a properly designed filter 26 consisting of inductances with condensers on each side is a very effective means for removing generator ripple. The negative terminal of 25 is connected to the neutral point on 23 while the positive terminal connects to the plate circuits of the three tubes as shown. The antenna circuit comprises the aerial 30, the ammeter 31, the secondary 28 of a power output transformer, the antenna tuning inductance 29, and a'key-click' elimicomplished by making its inductance, in

connection with the tube and circuit capacity in parallel with it, such that the primary circuit will choke or.approxima-tely choke over the adjustable wave-length range of the transmitter. When the antenna circuit is closed, however, and is brought into resonance with the frequency of the master oscillator, this choking effect in theprlmary is destroyed, the primary and secondary then acting like a power transformer. This transmitting circuit gives quiet transmission on constant frequency without harmonics, and there is no hum ue to dynamo ripple when tuning a receiver nearthe transmitter. A dial on variable inductance l7 may be calibrated to indicate directly the frequency on which the transmitter is operating. For any setting of 17 therefore, the plate current to' both the power amplifier tubes may be adjusted to the desired value by the coupling between 27 and 28 when 29 is adjusted so that the antenna is in tune with the master oscillator. For maximum plate circuit efliciency it is essential that primary coil 27 be designed to have the lowest possible distributed capacity, inasmuch as when the antenna circuit is brought into resonance such capacity would act as a shunt and cause a loss in power. After these adjustments are made, a substantial increase in efiiciency may be had by adjusting the resonant circuit 21. It is found-that a variable choking means lit) at this point offers a considerable improvement over a fixed choke, inasmuch as the frequency of the undesirable oscillations is found to differ with different settings of 17. Feeding the high voltage plate supply in parallel as shown, instead of in series with the voltage of the high frequency oscillations across27, reduces the maximum high potential on the tubes and thus higher than rated D. C. potentials may be employed. The circuit just described enables vacuum tubes to be run continuously at from two and one half to three times their rated out puts. It is found that plate circuit efii ciencies for the power amplifier tubes of 75 per cent is readily obtainable, and the overall efliciency of such a circuit is well above that of arc or spark transmitters. Vacuum tubes which have been especially designed to withstand high plate potentials have been found to give high plate circuit efficiencies and if used in this circuit would yield even better results than those enumerated.

The generators 22 and 25 may be direct connected on the same shaft with a driving motor 33 asindicated by the dotted line. In Fig. 1 such a motor generator would be included in 4 together with an automatic starter controlled through the grounded cable 11 from the operating position by switch 9, so that the closing or opening of 9 automatically turns on or off the previously adjusted transmitter.

Keying for telegraphy is from 10 as indicated in Fig. 1, also through the sheathed cable 11, and may be accomplished in any suitable manner which does not create an audible clicking in the receiving system. A satisfactory:method, referring again to Fig, 2, is by inserting condenser 35 bridged by resistance 36 inthe ground lead as shown,

and having such proportionsthat when relay 34 controlled through a battery from key 10, is opened the current in 31 drops to Zero, and verylittle sparking if any occurs at ,the relay contacts during transmission of signals.

The enclosing m grounded metallic sheathing 11 of all conductors passing between the transmitting and receiving circuits prevents direct carriage of transmitter high frequency energy along these conductors. Vhat stray transmitter high frequency energy passes along other adjacent metallic objects, such as gas-pipes, electric conduits, etc. I believe to mostly affect the receiving coil circuit by electrostatic coupling, inasmuch asthe electrostatic shielding, already referred to, removes the difliculty. 1 v

The preferred receiving circuit for this system is shown in Fig. 3, where 37 is the small receiving coil, movably directionally mounted, 38 an electrostatic shield, and 51 the coil tuning condenser. 42 represents a metal-box completely surrounding the re mainder of the receiving equipment; 39 are radio frequencyamplifiers, 40 a detector and 41 tone amplifiers. The shield 38 is con nected to 42 as well as is one side of the filament heating battery shown. The resonant loop circuit, is loosely coupled by condenser 47 to the input resonant circuit 45 of the high frequency amplifier. The output tuned circuit 46 of the amplifier is then loose coupled by condenser 48 to the input tuned circuit 49 of detector tube 40. Condensers 47 and 48 are completely shielded by partitions 45' of the metal box 42 to prevent any possi- I ble coupling between the circuits excepting by capacity coupling through the condensers as intended The high frequency transformers are designed to give max mum amplification over the adjustable wave length range of the receiving set and are shielded reception, condenser 52 being to bypass the high frequency by transformer and battery as shown. The tone amplifiers are transformer'coupled in the usual manner, but

transformer 53 is for the purpose of exeluding D. C. plate current from the telephone receivers 12for the purpose of eliminating key-click, as disclosed in my Patent 1,648,835, dated Nov. 8, 1927, entitled Two way radio communication system, if it is desired to operate the system break-in," as described inpatent to \Vare No. 1,379,144.,

tuned circuit 49 of the detector has the external adjustment indicated at 13 in Fig. l and may be desirable as a beats pitch regulator if this type of reception is used. The remainder of the circuit is self-explanatory. It is necessary that the metallic box 42 have good conductivity, which can be secured by using thicker metal if poor conductors are used. The holes through which the conductors to the coil aerial and head phones are brought out of the box 42 should be no larger than necessary.

To adjust this circuit to a given transmitting station the condensers 47 and 48 are first made quite large. This so broadens the ire-- quency rangeof the circuit as to permit of rough tuning by condensers 51 and 6 at the same time. To make a final adjustment, however, and to secure the maximum selectivity the coupling is made very loose by condensers 47 and 48 and the tuned circuits of the loop, 45, 46 and 49 are then readjusted to be ex actly in resonance with the incoming signal. Quite strong local oscillations in the detector circuit are found desirable for boats reception as this still further increases the selectivity. The probable reason for this is that spark interferences and other noises do no remain in phase with the local oscillations, which are too strong to be affected and are consequently reduced in loudness to a greater extent than is the beat note by increasing the strength of the local oscillations. The design of resonant circuits and the purity and degree of coupling between them is very vital in a receiver of this character and intended for duplex service. The ratio of in instead of full duplex. The condenser 6 of ductance to resistance of each resonant circuit should be as high as possible while the coupling should be either purely magnetlc, or purely electrostatic as shown, between the various resonant circuits, electrostatic coupling being preferred.

The receiving set just described has an overall sensitiveness probably equal or better than any practical receiving system in regular service, notwit'hstandin the diminutive dimensions of the collecting element 37, which is preferably one foot in diameter for duplexing with a transmitter in the same room. I have found that such a receiver operates without interference from a A k. w. transmitter at a distance of 35 ft. on a 10% difference in operating frequencies be-' tween the receiver and transmitter.

This receiver is also found to be operable in locations considered very undesirable or even unworkable for long distance reception, as for instance in factory buildings or other locations where there is considerable induction. This is because of the fact that no external influence can affect the receiving equipment, except via the loosely coupled resonant element 37, 51.

It is found that while ordinary loose coupled receivers will a parently exclude all but a narrow band of requencies, see curve A, that upon close inspection, see curve B, such sets do pass frequencies over quite a wide range although in comparatively infinitesimal amplitudes. Receiving sets now in use pick up sufficient energy on inside coils and even on battery leads, etc. passing away from the set box to make exclusion of strong interfering signals and other noises on frequencies widely differing from that to which the set is adjustedimpossible. Curve C is taken on a circuit like Fig. 3 with tighter than proper couplin s at condenserset'? and 48. It was found at trequencies outside those covered by the resonance curve that even a powerful transmitter in the same room would make no indication on a microammeter con nected into the detector circuit.

Figures 4, 5 and 6 show resonance curves obtained by plotting the value of current, in microamperes, in the detector circuit for a given tuning adjustment of the cycles per sec, of a nearby oscillator. In other words, the wave length of the nearby oscillator is varied from below the wave length for which the receiver is tuned, through the wave lengths which cause resonance in the receiver circuit and beyond the point where resonance occurs. The peak of the curves in Figs. 4-

and 6 show the wave length to which the receiver is tuned for best reception. Curve B, in Fig. 5, is a continuation of one side of curve A with the ordinate or current scale much enlarged. This curve shows that an unshielded receiving set will respond to wave lengths considerably beyond that to which it 'quency, whereby the said is tuned. This response has no effect on the head phones of thereceiver when the transmitted waves are radiatin a considerable distance away because of t e small amount of radiated energyv picked up by the aerial of the receiver, but when the receiver is located in the powerful field of the transmitting antenna, the energy picked up is sufiicient to effect the head phones even when the receiv ing circuit is tuned to a different wave length. l

Under these conditions, it is difficult to exclude the strong signals from the local transmitting station and to receive weak signals from distant stations. Applicant has sucmitting station, there is no current flowing in the detector circuit-if the receiver is tuned to a wave length approximately 10% either side of that of the local station.

Such a receiver is, therefore, highly selective and is adapted to pick up weak s1 nals from distantstations even when the ocal station is transmitting on a wave length at the limits noted above.

With transmittin and receiving equipment constructed and arranged as described, the operation of simultaneous duplex radio communication is greatly improved and simplified.

' I claim:

1. A radio receiving system ada ted for simultaneous operation with a nearby radio transmitter, and comprising in combination a coil aerial in circuit with a radio frequency amplifier, a detector, and signal indicating apparatus, means for narrowin the upper part of the resonancecurve of t e receiving system including loose coupling between said coil aerial, radio frequency amplif er and detector, and means, including closed circuited metallic shields enclosing said amplifier, detector and loose coupling, for causing the lower part of said resonance curve to come substantially to zero a predetermined distance to either side of the resonant frereceiving system will be substantiall unaffected by oscillations from the nearby transmitter having a frequency outside those covered by said resonance curve.

2. A radio receiving simultaneous operation transmitter,

system adapted for with a nearby radio and including a coil aerial'incircuit with a radio frequency amplifier, a detector and signal indicating means, means .for narrowing the upper part of the resonance curve of the receiving system including adjustable capacity coupling between said coil aerial, amplifier and detector, and means, including an electrostatic shield enclosing said coil aerial and closed circuited .to Zero a predetermined distance to either side of the resonantfrequency, whereby the said receiving system will be substantially unaffected by oscillations from the nearby transmitter having a frequency outside those unit, a radio frequency amplifier unit and a covered by said resonance curve.

3. In a radio receiving system adapted for simultaneous operation with a nearby transmitter, a coil aerial in circuit with a tunin condenser, means for elect-rostatically shielding said aerial and its tuning circuit, radio frequency amplifying means loosely coupled. to said coil aerial, a closed circuited metallic shield enclosing said amplifying means and .said coupling inseparate compartments, de-

tecting and audio frequency amplifying means loosely coupled to said radio frequency amplifying means, a closed circuited metallic shield enclosing said last-named coupling and said detecting and audio. frequency amplifying means in separate compartments, whereby to confine the resonance of said receiving system to a narrower band i of frequencies.

4. In a duplex radio communication systern having a transmitter and a receiver adapted for simultaneous operation on frequencies differing slightly from each other,

comprising in the receiver the combination of a receiving element, amplifying and detector circuits, loose couplings between the receiving element, amplifier and detector circuits, an electrostatic shield for the receiving element, separate closed circuited shields enclosing the amplifying and detecting circuits and a source of power and conductors therefore within certain of said shields.

5. A radio receivingsystem comprising in combination a loop receiving element, a radio frequencyamplifier and a detector, a loose coupling between the loop and the amplifi'er, asecond loose coupling between the amplifier and detector, and shielding means enclosing the amplifier, the detector and the couplings.

6. In a duplex radio communication system, in combination, a transmitter having a radiating antenna, a master oscillator and power amplifiers, means for setting the frequency of the transmitted waves and means for maintaining the frequency of said waves constantindependently of changes in the antenna circuit constants, a receiving set having a coil aerial, radio frequency amplifiers and a detector, means for couplin and shielding said aerial, amplifiers, and etector of the receiving set in such manner as to reduce theband of frequencies to which said set may respond for a gi'ventuning adjust- I ment whereby to permit duplex operation on a slight difference in the resonant frequencies of said transmitter and receiver.

, 7. A. radio receiving system comprising an antenna unit, a radio frequency amplifier unit, and a detector unit, loose capacity collplings disposed between said units, a closed circuited metallic shield enclosing all of said units except the antenna.

8. In a radio receiver having an antenna detector unit, the combination of loose capacity coupling means between said units to narrow the upper part of the frequency response curve and shielding means enclosing all parts except the antenna to cause the lower part of said curve to dro substantially to zero a predetermined d1stanceon either side of the peak of the curve.

9. A radio receiving system comprising an antenna, a multi-stageradio frequency amplifier having means for controlling and maintaining regeneration, a detector, audio amplifier and signal indicating apparatus, said radio frequency am lifier and detector including a. plurality o resonant circuits, closed circuited metallic shields enclosing all parts carrying radio frequency currents except the antenna, and coupling means disposed between the v'ariousportions of the circuit for narrowing the radio frequency response characteristic of the system.

1.0. A system for radio reception, comprising in combination an antenna, a radio frequency amplifier, potentiometer means therein controlling regeneration, a detector, anaudio amplifying and signal indicatinggapparatus, closed circuited metallic shields en.- closing all parts carrying'radio frequency currents except the antenna, and successively disposed coupling means also within said shields for further narrowing the band of frequencies to which the system will respond.

11.. A system for radio reception, comprising in combination an antenna, a radio frequency amplifier, adjustable regeneration means associated therewith, a detector, independent adjustable regeneration means associated therewith, an audio amplifying and signal indicating apparatus, closed circuited metallic shields enclosing all parts carrying radio frequency currents excepting the an tenna, and successivel disposed coupling means also within sai shields for further narrowing the band of frequencies to which the system will respond.

12. 1t system for receiving continuous 'wave telegraph signals comprising anantenna,a radio fre uency amplifier, potentiomet-er means t erein. for preventing internal oscillations and an adjustable oscillating detector, an audio amplifying and signal indicating apparatus, shielding means separately enclosing all parts of the apparatus excepting the antenna and coupling means disposed between the several portions of the apparatus for narrowing the radio frequency response characteristic of the system.

wave telegraph signals, comprising an an-\ 15 tenna, a radio frequency amplifier, pot enti ometer means therein for preventing internal oscillations and an ad'ustable oscillating detector, an audio amplifying and signal indicati'ng apparatus, shielding means enclos- V ing all parts of the apparatus excepting the antenna and coupling means disposed between the several portions of the apparatus narrowing the band of frequencies to which the system will res nd:-

141A duplex radio system comprising a loop receiving apparatus and aseparately excited power amplifier-vacuumtube transmittingapparatus, the loop being partially --shielded the receiving apparatus being com- IQ pletely shielded-and containing a radio hei fluency-amplifier and a plurality of loose couplings, the transmitting apparatus containing Ianiadjustable checking means in series with-the 85-: tubes r- 715. .Aiitiuplex radio system comprising a -loop-= receiv1ng apparatus and.a separately ;exc1ted poweramplifier vacuum tube transmitting apparatus, the receiving apparatus 40L being completely shielded and containing a radio frequency amplifier and a plurality of loose 'couplings, ithe loop being partiallyand havin "an area of approxi .mately one uare oot.' j 51 16: In com ination witha radio receiv- "iin systenihavinga'collecting element, a

ra. in frequency amplifier in circuit therewith, means for 'reventinginternal oscillations'in said amp ifier, a detector and signal indicating means, and means for increasing the select vity comprising means for narrow- ,ing the frequency response curve, and shielding means for excluding undesired strong signals. l 55 17. In combination with a radio receiving system havinga collecting element, a radio frequency amplifier" incircuit therewith,

means for preventing internal oscillations in said amplifier, a detector and signal indicato0 ing means, and means forincreasing the selectivity comprising means for narrowing the frequency response curve, and shielding system for receivirig continuous means 1 for signal:

grids of 'the poweramplifier ingby way of sai collecting element.

18. In combination with a radio receiving system having a resonant collecting element,

a radio frequency amplifier in circuit therewith, means forpreventing internal-oscillations 1n said amplifier, a detector and signal indicating means,'and means for increasing ing thefrequency response curve, and shieldthe selectivity comprising means for narrowing means for excluding undesired strong signals. 19. vIn combination with a radio receiving system having a'collecting element, aradio frequency amplifier in; circuit therewith,

means for reventing internal oscillations in said ampli' er,a detector and signal iridicating means, and means for-increasing the selectivity comprising a plurality of ,resonance and coup ng'nieans'for narrowin the frequency response curve, and shie dlng excluding, undesired strong 4 20. In-combinationwith a radio receiving system having acollecting element; a radio. frequency. amplifier in -"cir cuititharewith,

means for reventing internalpscil-lations in said ampli er, a detector and signal indicat-,

ing means, a and means 'forincreasing, the

selectivity com rising a plurality of resonance and coup ing means forna-rrowing-the frequency response curve, andshielding .r

-means,preventing, ick-up ofrsignalsexcept ing bywayof sai dcolleetingeleinent. '21. A system for receivingv continuous.

wave telegraph signals, comprisingan an- Y tenna, a radio frequency amplifier, detector, and audio amp ifying on signal indicating apparatus, means for providing independent oscillations enabling heterodyne receptiomnand means for increasing the selectivity comprising 'a vplurality of resonant circuits within the apparatus for narrowing the band of frequencies to which the system will respond, and means shielding the said amplifier and detector.

- 22, A system -forreceiving continuous ll0 wave telegraph signals, comprising an antenna, a radio'frequencyamplifier, a detector, and-audio amplifying-and signal indicating apparatu means ;for' providing independent oscillations enabling heterodyne reception, and means for increasing the selectivit com risingaplurality of-resonance an coup ing means for narrowing the .band of fr uencies to whichfthe system will res ond, an means an detector.

Signed at ,New

shieldingthe amplifier York, in the county of New York and State of New York, this 30th day of June A. D. 1922. i

. 7 PAUL 

